This invention relates to a blow molding apparatus, and more specifically, to blow clamps for securing an opposed pair of moveable platens to one another during blowing.
In the blow molding of plastics to make containers and other articles, a xe2x80x9cparisonxe2x80x9d or xe2x80x9cpreformxe2x80x9d is first clamped between mold halves mounted to opposite platens of a blow molding machine. Pressurized air is then introduced into the parison or preform to cause it to stretch, through inflation, to conform to a mold surface defined between the mold halves. The blown part is allowed to cool, the mold halves separated and the blown part removed.
During blowing, the opposite halves of the blow molding machine are held together by a xe2x80x9cblow clampxe2x80x9d which both locks the two halves together and applies a force urging the two halves toward one another to counter blowing forces acting to separate the mold halves. Although a fluid pressure actuable cylinder may be used for the blow clamp, this is not an ideal arrangement as the necessary clamping forces require a rather substantial cylinder which is relatively slow and energy inefficient for most of its stroke which requires simply opening and closing the blow mold rather than applying a clamping force. Preferably also the blow clamp should separate upon mold opening so as not to interfere with the removal of blown parts. This is not possible with a fluid pressure actuable cylinder. PCT application PCT/EP96/02507 illustrates and describes a novel clamping arrangement with certain unique advantages. The clamping arrangement includes rows of teeth on the machine tie bars which can be moved into and out of engagement with corresponding rows of teeth on respective clamping nuts. The tie rods are rigidly secured to one platen and the clamping nuts to the opposite platen. The tie rod nuts are provided with rotation means and axial force means. The clamping process involves first rotating the tie rods to engage the clamping nuts and then applying, via a hydraulically actuated piston, an axial force to the tie rods which is transferred to the opposite platen through engagement between the corresponding teeth on the tie rods and the clamping nuts.
The arrangement described in the above PCT application does have a couple of drawbacks. Firstly, the teeth on the tie bars are part way along the tie bars, toward the middle of the tie bar and accordingly, the ends of the tie bars remain in the clamping nuts even when the mold platens are moved apart. This poses interference problems with any stripping apparatus. Additionally, application of rotational and axial forces to the tie rods requires a significant amount of torque to overcome the friction resisting rotation caused by the hydraulic seals in the piston associated with the clamping nut. Furthermore, the entire tie rod assembly is quite complex and expensive to manufacture as it includes apparatus for rotating the tie rods, separate apparatus for taking up clearance between the interengaging teeth and still further apparatus for applying the clamping force.
It is an object of the present invention to provide a blow clamp arrangement which separates to enhance access to the associated blow molds for loading and stripping purposes.
It is a further object of the present invention to provide a blow clamp arrangement which does not require both rotational and axial movement of the tie rods.
It is a still further object of the present invention to provide a blow clamp arrangement which doesn""t require any rotation of any hydraulically actuable piston or cylinder components for engagement and disengagement.
A blow clamp for a blow molding apparatus having first and second platens movable between a closed and an open position. The blow clamp includes at least two clamping piston nuts secured to the first platen and respective tie bars secured to the second platen for registering with the clamping piston nuts. The tie bars are movable between an engaging and a disengaging configuration. In the engaging configuration the tie bars are secured against axial movement relative to the clamping piston nuts. In the disengaging configuration, the tie bars are freely axially movable relative to the clamping piston nuts. An actuator is provided for moving the tie bars between the engaging and the disengaging configurations. A clamping force applicator is associated with the clamping piston nuts for applying an axial closing force to the clamping piston nuts. The clamping piston nuts and tie bars may have radially extending teeth which engage in the engaging position and do not engage in the disengaging position.
The actuator may cause the tie bars to rotate. A single actuator may rotate more than one tie bar simultaneously either through direct connection or through linkage interconnecting a plurality of tie bars. The actuator may be a motor or a hydraulically actuable piston.
The clamping piston nuts may include a fluid pressure actuable piston for applying the axial closing force to the clamping piston nuts.
Preferably, the clamping piston nuts and tie bars separate during mold opening by an amount sufficient to permit passage of a pallet track therebetween.